Negative feedback amplifier circuit



June 1950 E. E. CARPENTIER 2,510,633

NEGATIVE FEEDBACK AMPLIFIER CIRCUIT Filed April 2'7, 1946 r INVENTOR. EDM ND EGBERTUS CARPENTIER AGENT Patented June 6, 1950 QFF-EQE v I V 2510,689- I I I NEGATIVEEEEDBACK AMBLIEIEB, CIRCUIT EdinondEgb'erths -Garpentier; Eindhcven; N etherlands; assignor; liy mesneassignments; .to'Hart-- ford NationabBank and Trust Gompany;.I-Iarte fnrdl.onn.,aatmstce lipplicatibn-Aprilfifl, 1946, Serial No. 665,393 In the Netherlands September 25, 1942 lfllaims... (01. 1791-171}. I

inventionmelateswtor arr-amplifying circuit.-

arrangement. in. which; for: the? purpose of; decreasing; the distortion. which; occurs; in, the-:circuit. use 1 is made: of; negative feed-back: I comprising an amplifying tube; whose;- input circuitt'hassupplied; to it the, voltage; to.- be 1 amplified;v and whose-anode;circuitjandlcathode-:circuiti-eachtin, clude an impedance, preferably; a; resistance; which -.imp edances are:c.onnectedtmthe-input circuits of two push-pull connected amplifying tubes in such manner that; the-:vcltages. set up at the said impedances control .thesetubesinpushepull. the amplifi'edoutput voltage beingitakenofiifrom the output circuit of these tubes. By the term cathode circuit we mean in=this-case'the common. part of the anode circuit and of the grid circuits. 7

.A circuit arrangement Vo f this;v kind is: shown 1 of, the accompanyingr d awing: The circuit arrangement shown in this figure comprises an amplifying tube I whose control grid has a voltage to be amplified, supplied to it via input terminals 2 and 3 and Whose anode circuit and cathode circuit include resistances 4 and 5 respectively of equal value. The anode and the cathode of tube I are connected in the usual manner to the control grids of two push-pull connected amplifying tubes I5 and I1 respectively via coupling condensers I and 9 and leakage resistance II and I3 respectively, due to which on controlling tube I the voltages set up at the resistances 4 and 5 control the tubes I5 and I! in push-pull. The anode circuits of these two tubes include the primary winding 2| of an ordinary push-pull transformer I9, which transformer comprises, in addition, a secondary winding 23 from which an amplified output oscillation is derived.

Tube I is connected in accordance with the so-called cathodyne arrangement, with the aid of which an alternating voltage asymmetrical relatively to ground is converted into a symmetrical voltage. A known property of this circuit consists in the whole voltage set up at the oathode resistance being supplied to the control grid of the amplifyin tube in anti-phase with the input voltage to be amplified, in other words tube I has negative feed-back, resulting in an appreciable decrease of the distortion which occurs in this tube. Another consequence of the negative feed-back coupling is, however, that the voltage set up at the cathode resistance 5 can at most become equal to the input voltage, in other words an amplified voltage is not set up at this resistance. In' addition, in view of the push-pull the anode-resistance 4; musthaveayaiue equ l to. that of; theecathode;resistanceeli solthatonlm tubesdssnotdecreased.

object. ofthe invention. is to. provide.- improvement .of; the. circuitarrangementsto ,which the, invention has reference whereby negative feedback. is incorporated in the, circuit; under.

the. tube-s15 andulil.

Accordin to; the invention,- this-.- improvement consists. in. a; negative. feedbackv voltage: or. cur rent derived from.theoutputcircuit ofzthepush pull connected tubes bein supplied to the cathode circuit of the first-mentioned amplifying tube and the cathode impedance of this tube being given a lower value than the anode impedance.

The invention will be set out more fully by reference to the accompanying drawing showing, by Way of example, one form of construction of c conditions, unchanged, as; regards. amplification:

' a circuit arrangement according to the invention.

tube I are in anti-phase with the input voltage of tube 1 the two first-mentioned voltages are consequently in phase and support each other, that is to say the anode current of tube I flowing through the resistance 5 is increased by the negative iced-back current flowing through the resistance 21. Consequently, the voltage drop at the resistance 5 required for the push-pull control of tube I1 is obtained at a lower value of this resistance than in the circuit shown in Fig. 1, that is to say that in the circuit according to the invention the cathode resistance 5 of tube I must be smaller than the anode resistance 4.

In the circuit shown in Fig. 2 the portion of the output voltage of tube I which is thus fed back to the input circuit of this tube is smaller than in the circuit of Fig. 1, but on the other hand a portion of the output voltage of tubes I and I1 is also fed back to the said input circuit, so that unlike Fig. 1 these tubes have also negative feed-back. This result is achieved with the circuit arrangement according to the invention without any decrease in amplification of tube I relatively to the circuit of Fig. 1. In fact, the anode resistance 4 can remain unchanged, while in spite of the lower value of the cathode resistance 5 again as great a voltage is set up at this resistance as at the resistance 4, so that the voltage amplification of tube l in the circuit shown in Fig. 2 is also 2:1.

What I claim is:

1. An amplifier circuit arrangement comprising a first electron discharge tube having a cathode, a grid and an anode, an anode impedance element coupled to said anode, a cathode impedance element having an impedance value smaller than that of said anode impedance element and being coupled to said cathode, means to apply signals to be amplified to the grid of said first tube to produce a first output voltage across said anode impedance element and a second output voltage across said cathode impedance element in anti-phase with respect to said first output voltage, a second and a third electron discharge tube each having a cathode, a grid and an anode and being connected in pushpull amplifying relationship, means to couple the grid of said second tube to the anode of said first tube to apply said first output voltage thereto, means to couple the grid of said third tube to the cathode of said first tube to apply said second voltage output thereto, and means to couple the anode of said second tube to the cathode of said first tube to connect said first and said push-pull connected tubes in negative feedback relationship thereby to produce an output sig- 4 nal substantially proportional to said applied Sig nals.

2. An amplifier circuit arrangement comprising a first electron discharge tube having a cathode, a grid and an :anode, an anode resistor coupled to said anode, a cathode resistor having a resistance value smaller than that of said anode resistor and being coupled to said cathode, means to apply signals to be amplified between the grid and cathode of said first tube to produce a first output voltage across said anode resistor and a second output voltage across said cathode resistor in anti-phase with respect to said first output voltage, a second and a third electron discharge tube each having a cathode, :a grid and an anode and being connected in pushpull amplifying relationship, means to couple the grid of said second tube to the anode of said first tube to apply said first output voltage thereto, means to couple the grid of said third tube to the cathode of said first tube to apply said second voltage output thereto, and means comprising a resistor coupling the anode of said second tube to the cathode of said first tube to connect said first and said pushpull connected tubes in negative feedback relationship thereby to produce an output signal substantially proportional to said applied signals.

EDMOND EGBERTUS CARPEN'I'IER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,506 Yeutter Dec. 28, 1937 2,215,439 Root Sept. 17, 1940 2,361,198 Harmon et :al. Oct. 24, 1944 

